bobbin trouble.
 

I am having trouble with the thread from the bobbin. I am able to sew for a short time but then the thread will get all knotted up. I check and I see that the thread from the bobbin thread is no longer threaded and it makes the tension very loose which I know is making the knots.

Don't know what kind of machine you have, but there is a tension spring in the bobbin case. Either it has loosened a bit and needs to be tightened or there is a bit of lint stuck in the spring causing it to be too loose. Look in your manual to find how to clean the bobbin case.

I have had the tiny pieces of thread stuck in my bobbin case more than once. Sometime they can be hard to get out but they have to come out in order to sew correctly. I have this happen on both top and front bobbin cases, by the way. On older and newer machines.

What brand and model of machine do you have? Does the bobbin have a bobbin case, or is it a drop-in bobbin?

PaperPrincess gave great suggestions. If you have a bobbin case, try tightening the tension 1/4 turn at a time. Clean & your bobbin compartment with a small brush & oil where indicated. When I can't find my little brush sometimes I just use a long pin that I dampen with a wet paper towel to grab the dust bunnies & then wipe the pin on in each time it grabs some dust. If you have a bobbin case, check for any little burrs that could be shredding or cutting the bobbin thread -- which would then create a thread nest (same thing that happens if you don't pull up your bobbin thread to the top of your fabric before you start sewing).

And, of course, it's always possible that it's the thread itself that's causing the problems. Try a newer or better quality thread & see if it still happens. If you're on a budget, I'd go with either a 100% poly thread or Gutermann cotton thread.

Id switch off unthread everything and clean all thread channels. Take extra time on the bobbin area. I use a paint brush it gets into parts the pin or q tip can.

I pinched one of the inter den brushes used by son when he wore braces, it's great for getting into all the little nooks and crannies and grabbing dust and thread.

Have you had your machine in for servicing? I know it is time for my Bernina to go in, it is just getting time for a friend to take me there.

PaperPrincess is correct it might be as simple as the spring or even lint in the bobbin area . I was recently having the same issues with my most recent machine which has a drop in bobbin (all my others have a front loading bobbin). The entire bobbin assembly popped right out when the stitch plate was removed - who knew that that much lint could accumulate in such a small spot? Once I vacuumed it out it has sewn perfectly ever since. Check your manual to see how to clean the area.

I'm not understanding whether the tension is loose on the top or the bottom thread? Sometimes when my top thread jumps out of the take up spring (usually cause it gets caught in the bobbin area due to a stray thread or lint) it will create a mess and a loose top tension. Also, are your bobbins getting wound nice and solid, instead of spongy? And have you trimmed off the little tail left when you wind one (from the top hole)? I've been mentoring high school kids making quilts and they have trouble winding those nice solid bobbins and it's caused lots of tension issues.